Cloud Microphysical Processes and Atmospheric Water Budget during the 20 July 2021 Extreme Precipitation Event in Zhengzhou, China

This study investigated the cloud microphysical processes and atmospheric water budget during the extreme precipitation event on 20 July 2021 in Zhengzhou of Henan Province, China, based on observations, reanalysis data, and the results from the high-resolution large-eddy simulation nested in the Weather Research and Forecasting (WRF) model with assimilation of satellite and radar observations. The results show that the abundant and persistent southeasterly supply of water vapor, induced by Typhoons In-Fa and Cempaka, under a particular synoptic pattern featured with abnormal northwestward displacement of the western Pacific subtropical high, was conducive to warm rain processes through a high vapor condensation rate of cloud water and an efficient collision–coalescence process of cloud water to rainwater. Such conditions were favorable for the formation and maintenance of the quasi-stationary warm-sector heavy rainfall. Precipitation formation through the collision–coalescence process of cloud water to rainwater accounted for approximately 70% of the total, while the melting of snow and graupel accounted for only approximately 30%, indicating that warm cloud processes played a dominant role in this extreme rainfall event. However, enhancement of cold cloud processes promoted by latent heat release also exerted positive effect on rainfall during the period of most intense hourly rainfall. It was also found that rainwater advection from outside of Zhengzhou City played an important role in maintaining the extreme precipitation event.